Injection mold for optical discs

Abstract

An injection mold for optical discs has a stamper mounted on any one of mold surfaces defining a mold cavity, a cylindrically shaped center pressing member being inserted into and engaged with a center portion of the stamper, and a cylinder piston being placed at a center portion of the mold and movable in forward and backward directions by a fluid pressure in relation to the center pressing member so as to make the center pressing member in contact with the top of the cylinder piston whereby the stamper is detachably mounted on the mold by the center pressing member. The injection mold for optical discs is characterized in that a plurality of crews are provided on the center pressing member at its contact portion to the cylinder piston at circumferentially constant pitch and projections to be engaged with the crews are provided on the top of the cylinder piston, wherein the crews of the center pressing member, the projections and grooves of the cylinder piston, a receiving surface of the mold for positioning the insertion position of the center pressing member with reference to the mold are placed in concentric circle.

What is claimed is: 
     
       1. An injection mold for optical discs comprising: a movable mold having a molding surface and a receiving surface;   a stamper being mounted on the movable mold molding surface, and having a center portion and further defining a mold cavity;   a cylindrically shaped center pressing member having an upper portion and a lower portion, the upper portion engaging the center portion of the stamper and the lower portion contacting at least a portion of the receiving surface of the movable mold; and   a cylinder piston being placed at a center portion of the movable mold and movable in a forward direction and a backward direction by a fluid pressure in relation to the center pressing member, the cylinder piston having a top portion being in close proximity with the center pressing member;   a plurality of crews extending downward from the lower portion of the center pressing member and being at a circumferentially constant pitch;   projections extending from the top portion of the cylinder piston and engaging the plurality of crews;   grooves being formed substantially by a bottom surface of the center pressing member and a top surface of the cylinder piston,   the crews, the projections, the grooves and the receiving surface being placed in a concentric circle, and   the stamper being detachably mounted on the mold by the center pressing member when the cylinder piston moves in the forward direction.   
     
     
       2. The injection mold as claimed in claim 1, further comprising: a stationary mold opposing the movable mold;   an inserter being inserted into at least one of the movable mold and the stationary mold, the stamper being mounted on the inserter;   a sealing member being provided proximate to the center pressing member, the center pressing member being inserted into and tightly fitted via the sealing member to an inside portion of the inserter; and   an air passage being provided on the inside of the inserter and supplying a releasing air introduced through a gap between the center pressing member and the cylinder piston and a cavity defined between the movable mold and the stationary mold wherein   the center pressing member has substantially constant cross sectional area between the upper portion and the lower portion.   
     
     
       3. The injection mold as claimed in claim 2, wherein the sealing member is an O-ring. 
     
     
       4. The injection mold as claimed in claim 2, wherein the sealing member surrounds a peripheral portion of the center pressing member. 
     
     
       5. The injection mold as claimed in claim 1, further comprising an air passage within the movable mold. 
     
     
       6. The injection mold as claimed in claim 1, further comprising a fixing ring member being provided on a peripheral portion of the stamper. 
     
     
       7. The injection mold as claimed in claim 6, further comprising a superimposing ring member being superimposed on the fixing ring member. 
     
     
       8. The injection mold as claimed in claim 1, wherein a resin pressure in the injection mold is transmitted through the center pressing member to the receiving surface of the movable mold. 
     
     
       9. The injection mold as claimed in claim 1, wherein the center pressing member projects from the molding surface when the cylinder piston moves in the forward direction. 
     
     
       10. The injection mold as claimed in claim 1, further comprising: a center pin engaging a center portion of the injection mold;   an extrusion sleeve holding the center pin; and   a center sleeve substantially surrounding the extrusion sleeve, the center pressing member being fixed to the center sleeve.   
     
     
       11. The injection mold as claimed in claim 1, wherein an inner diameter of the stamper is substantially the same diameter as an outer diameter of the center pressing member. 
     
     
       12. An injection mold comprising: a movable mold having a stamping surface and a receiving surface positioned substantially parallel to the stamping surface;   a stamper provided on the stamping surface of the movable mold;   a center pressing member having a uniform cross sectional area, a lip and bottom surface, the lip engaging the stamper and the bottom surface contacting at least a portion of the receiving surface of the movable mold;   at least one hooked shaped crew extending from the bottom surface of the center pressing member; and   a cylindrical piston being placed at a center portion of the movable mold and movable in a forward direction and a backward direction by a fluid pressure in relation to the center pressing member, the cylindrical piston having a top surface; and   projections extending from the top surface of the cylindrical piston and engaging the crews,   the stamper detaching from the center pressing member when the cylindrical piston moves in the forward direction, and   the crews, the projections and the receiving surface being placed in a concentric circle.   
     
     
       13. The injection mold as claimed in claim 12, further comprising: an inserter being mounted into the movable mold and holding the stamper;   a sealing member being provided proximate to the center pressing member, wherein the center pressing member is inserted into and tightly fitted to an inside portion of the inserter.   
     
     
       14. The injection mold as claimed in claim 13, wherein the sealing member surrounds a peripheral portion of the center pressing member. 
     
     
       15. The injection mold as claimed in claim 12, further comprising an air passage within the movable mold.